The 4-aminoquinoline drug hydroxychloroquine (HCQ) is reported to be as active as chloroquine (CQ) against falciparum malaria, and less toxic. Existing prophylactic regimens for areas where there is CQ-resistant malaria recommend CQ with proguanil as an alternative where none of the three preferred regimens (atovaquone-proguanil, doxycycline or mefloquine) is thought suitable. In such cases, toxicity is likely when CQ-proguanil is administered to persons being treated for autoimmune disease with daily HCQ. The question therefore arises whether in such circumstances HCQ could effectively replace the CQ component of the prophylactic combination. We confirmed similar activity of CQ and HCQ against CQ-sensitive Plasmodium falciparum, but found that whereas HCQ in vitro was 1.6 times less active than CQ in a CQ-sensitive isolate, it was 8.8 times less active in a CQ-resistant isolate. The result can also be predicted from an analysis of the physicochemical properties of CQ and HCQ. To give limited protective effect similar to 300 mg CQ base weekly against CQ-resistant P. falciparum would demand daily doses of HCQ above the recommended safe level. These observations contraindicate the use of HCQ in prophylaxis or treatment of CQ-resistant falciparum malaria. Where CQ-proguanil prophylaxis is the only option available in a patient on high-dose HCQ treatment, visiting a CQ-resistant area, replacement of the anti-inflammatory regimen by a daily CQ course at a suitable dose should be considered.

Since its introduction over a decade ago, confocal microscopy has found wide applicability in the microscopy of thick specimens and living tissue because of its ability to obtain images from deep inside the sample without interference from scattered or out-of-focus light. Three new instruments that are capable of imaging optically dense specimens such as the skin are considered here: a modified tandem-scanning confocal, the video-rate laser-scanning confocal microscope (both of which were developed specifically to examine skin in vivo), and the two-photon laser-scanning microscope, a design which is "inherently confocal." The tandem-scanning and video-rate confocals use visible and infra-red light, respectively, to acquire reflection images, whereas the two-photon scanner is a fluorescence microscope. The advantages and drawbacks of each of these instruments is considered.

Purpose. To visualize the transport pathway(s) of high molecular weight model compounds across rat nasal epithelium in vivousing confocal laser scanning microscopy. Furthermore, the influence of nasal absorption enhancers (randomly methylated β-cyclodextrin and sodium taurodihydrofusidate) on this transport was studied.

Purpose. (1) To determine the extent of iontophoretic transport as a function of molecular weight (MW) of the penetrant; and (2) to visually and quantitatively characterize the iontophoretic transport pathways (follicular (F) versus nonfollicular (NF)) of the fluorescently-labeled poly-L-lysines employed.

The effects of non-ionic surfactant vesicles (NSVs) on human skin in vitro were studied in relation to the physico-chemical properties of the vesicles. The interactions between NSVs and skin were visualized using both freeze fracture electron microscopy and confocal laser scanning microscopy. The physico-chemical properties of the NSVs were varied in a systematic way, using a broad series of polyoxyethylene monoalkyl ether type surfactants (CnEOm). The number of oxyethylene units (m) was varied between 3, 7 and 10, and the number of carbon atoms (n) was either 12 or 18. Both the effects of liquid state vesicles composed of C12Eo3,7 and C9=9EO10 surfactants and gel state vesicles (C18EO37) were investigated. After the application of the NS V suspension on the stratum corneum surface two essentially different types of vesicle-skin interactions were visualized. Firstly, an interfacial interaction, involving the adsorption of vesicles, and the deposition of bilayer sheets on the outermost layers of the stratum corneum observed for all NSV formulations tested in this study. Secondly, effects on the ultrastructure of the stratum corneum were observed: the appearance of water pools observed for the liquid state vesicles only, and ultrastructural changes of the intercellular lipid domains are induced only observed after treatment with C12EO3 NSVs. Neither changes in the ultrastructure of the viable epidermis, nor changes in deeper skin layers were observed.

The aim of this study was to characterize transport of FITC-labeled dextrans of different molecular weights as model compounds for peptides and proteins through buccal mucosa. The penetration of these dextrans through porcine buccal mucosa (a nonkeratinized epithelium, comparable to human buccal mucosa) was investigated by measuring transbuccal fluxes and by analyzing the distribution of the fluorescent probe in the epithelium, using confocal laser scanning microscopy for visualizing permeation pathways. The results revealed that passage of porcine buccal epithelium by hydrophilic compounds such as the FITC-dextrans is restricted to permeants with a molecular weight lower than 20 kDa. The permeabilities of buccal mucosa for the 4- and 10-kDa FITC-dextran (of the order of 10−8 cm/sec) were not significantly different from each other or from the much smaller compound FITC. The confocal images of the distribution pattern of FITC-dextrans showed that the paracellular route is the major pathway through buccal epithelium.

The effects of penetrant properties (lipophilicity and charge) and of vehicle pH on the iontophoretically enhanced delivery of amino acids, their N-acetylated derivatives, and eight tripeptides, of the general structure alanine-X-alanine, have been examined in vitro. The penetrants were (a) 9 amino acids (five were zwitterionic, two positively charged and two negatively charged), (b) four N-acetylated amino acids, which carry a net negative charge at pH 7.4, and (c) peptides which were blocked both at the carboxyl terminus using the mixed anhydride reaction with t-butylamine, and at the amino terminus by acetylation with 14C-acetic anhydride; the central residue (X) was varied widely by selecting one of five neutral amino acids, two negatively chargeable moieties (aspartic and glutamic acids), and a positively chargeable species (histidine). Iontophoresis at constant current (0.36 mA/cm2), using Ag/AgCl electrodes, was conducted across freshly excised hairless mouse skin. The diffusion cells used were designed so that both anode and cathode were situated on the same (epidermal) side of a single piece of skin. Overall, it was found that the results of this research support the principle of enhanced peptide delivery across the skin by iontophoresis.

Transdermal drug delivery has attracted considerable attention in recent years and the potential advantages of this mode of administration have been well documented [1]. The transdermal delivery of peptides and small proteins is of particular interest, since percutaneous administration overcomes many of the problems associated with conventional means of administering these potent therapeutic agents. The major obstacles to the passive permeation of peptidic agents are their hydrophilicity and size; however, therapeutically significant dosage levels have been achieved in vivo using either electrical or chemical enhancement.

The effects of penetrant properties (lipophilicity and charge) and of vehicle pH on the iontophoretically enhanced delivery of amino acids and their N-acetylated derivatives have been examined in vitro. The penetrants were nine amino acids (five were zwitterionic, two positively charged, and two negatively charged) and four N-acetylated amino acids, which carry a net negative charge at pH 7.4. Iontophoresis at constant current (0.36 mA/cm2), using Ag/AgCl electrodes, was conducted across freshly excised hairless mouse skin. Iontophoretic flux of the zwitterions was significantly greater than passive transport. Delivery from the anode was greater than from the cathode for all zwitterions. The level of enhancement was inversely proportional to permeant octanol/pH 7.4 buffer distribution coefficient. Cathodal iontophoresis of the negatively charged amino acids and of the N-acetylated derivatives produced degrees of enhancement which were significantly greater than those measured for the “neutral” zwitterions. Furthermore, the enhanced flux reached a steady-state level within a few hours for the negatively charged species, whereas the transport of the zwitterions continued to increase with time. Anodal iontophoresis of histidine and lysine, the two positively charged amino acids studied, induced substantial enhancement which was sensitive to the pH of the delivery vehicle. For example, the flux of histidine from an applied solution at pH 4 (where the amino acid carries a net positive charge) was significantly greater than that from a vehicle at pH 7.4 (where histidine is essentially neutral). The behavior of lysine was more complex and suggested a certain degree of neutralization of the skin's net negative charge.

This report describes a new iontophoretic diffusion cell that allows both electrodes to be applied to the same side of the same piece of skin. The cell permits a better approximation of the in vivo situation than do conventional side-by-side cells. The unique construction of the cell allows nonliquid material to be applied to the skin surface and makes it possible to investigate horizontal transport paths. Preliminary results utilizing the cell are described. Iontophoretic enhancement of morphine and clonidine delivery across full-thickness hairless mouse skin has been achieved. The importance of pH control in these experiments is apparent. Further experiments with morphine indicate that, for this drug at least, iontophoretically driven lateral transport within the skin is unimportant. Because the cell design allows significant parallels to the use of iontophoresis in vivo, we suggest that it will prove to be a useful tool in the determination of fundamental structure/transport relationships under the influence of an externally applied current.